How to convert data type for list of tuples string to float

With the 'a' value (ie a value not convertible to float) included, you can do, relying on this answer:

def tofloat(price):
    try: return float(price)
    except ValueError: return price #we do this when price is not convertable to float

After, proceed with a list comprehension:

result = [(item, tofloat(price)) for item, price in g]

result will be:

[('Books', 10.0), ('Pen', 10.0), ('test', 'a')]

There is no difference between float 10 and 10.000, so if you want 10 and 10.000 to appear in distinct ways you should keep them strings.

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Reflection on comments

To check that the numerical values are float and not int, we can do:

print([type(number) for item, number in result])

giving an output:

[<class 'float'>, <class 'float'>, <class 'str'>]

as required.

Notebook avaliable here.

you have a problem in your code because the x that you are using is a tuple. The elements of the list you provided are tuples type (String,String) so you need one more iteration on the elemts of the tuples. I have modified your code to :

newresult = []
for tuple in result:
    temp = []
    for x in tuple:
        if x.isalpha():
            temp.append(x)
        elif x.isdigit():
            temp.append(int(x))
        else:
            temp.append(float(x))
    newresult.append((temp[0],temp[1]))
print(newresult)

I have tested the code :

 //input 
 result= [('Books', '10.000'),('Pen', '10'),('test', 'a')]
 //output
 [('Books', 10.0), ('Pen', 10), ('test', 'a')]

You need to use the right value from each tuple:

for first_value, second_value in result:    
    if isinstance(second_value, int):
        ...
    else isinstance(second_value, float):
        ...
 

1. first_value will be "Books"
2. second_value will be '10.000'

But it's not clear what you are trying to accomplish.